A method of the generic type and a control program of the generic type are known from German Patent Application DE 197 28 814 A1. Various temperature levels are to be set in a cooling system for an internal combustion engine of a motor vehicle. The temperature levels which are to be set here are the reference variables for a fan control which determines the necessary power of the fan using a control program. The power of fan is determined here from the operating parameters of the cooling system, the predefined reference variable. Also from characteristic diagrams and characteristic curves of the fan motor. The operation of the fan is interrupted here until the coolant in the cooling system has reached and exceeded a minimum temperature. The intention here is to ensure that the internal combustion engine reaches the operating temperature as quickly as possible and that a cooling effect of the fan cannot occur prematurely. Once the fan function has been enabled, the control program adapts the power of the fan to the temperature level to be set. In particular two temperature levels of 90 degrees Celsius and of 108 degrees Celsius to which the power of the fan is to be adapted are provided here.
The abovementioned control of the power is thus an efficient method for reaching as quickly as possible the temperature levels which are predefined as reference variables. However, disadvantages result if the intention is to change over from a high temperature level to a low temperature level. The changing of the temperature level is in fact predefined by the changing of the reference variable for the control of the power. This reference variable changes here from 108 degrees Celsius to 95 degrees Celsius. For the control of the power of the fan motor this means that owing to the large temperature difference when the reference variable is changed from a high value to a low value it detects a large temperature difference with respect to the current actual temperature which is to be compensated as quickly as possible. This means that the fan motor whines at maximum power. This has the advantage that the lower temperature level is reached as quickly as possible, but is generally neither desirable nor necessary. The whining of the fan motor therefore leads to noise pollution and to unnecessary consumption of energy.
This is where the invention comes into play. The object of the invention is in fact to prevent whining of the fan motor when the temperature level to be set changes from a high value to a low value.